Shutter control of illumination of photoelectric transducer within light-transmitting block



K. KORMO SHUTTER CONTROL OF ILLUMINAT Aug. 26, 1969 s 3,463,931

ION 0F PHOTOELECTRIC TRANSDUCER WITHIN LIGHT-TRANSMITTING BLOCK Filed May 16, 1967 INVENTOR KALMAN KORMOS BY 6 Mi ATTORNEYS oai uhaswa United States Patent 3,463,931 SHUTTER CONTROL OF ILLUMINATION 0F PHOTOELECTRIC TRANSDUCER WITHIN LIGHT-TRANSMITTING BLOCK KalmanKormos, North Scituate, R.I., assignor to General Signal Corporation, a corporation of New York Filed May 16, 1967, Ser. No. 638,946 Int. Cl. G01d /34 U.S. Cl. 250-431 8 Claims ABSTRACT OF THE DISCLOSURE A photoelectric motion transducer including a light source, at least one photocell, and a movable element for controlling illumination of the photocell by the source. Interposed between the photocell and the illumination control element is a block of transparent, lightconducting material having a light-diffusing surface across which the control element causes light rays to move in a predetermined path.

BACKGROUND OF THE INVENTION This invention relates to photoelectric motion transducers.

One of the simplest devices of this type comprises a light source, a photocell, and a vane which moves with the part whose motion is to be transduced and which varies the area of the active face of the photocell which is illuminated by the source. The transducer is attractive because of its low cost and simplicity, and also because it imposes no mechanical load on the moving part. However, the device does have two disadvantages which limit its utility. First, since the power dissipation and current ratings of the photocell are based on uniform illumination of its active face, and the cell in the transducer just described is illuminated uniformly only when the vane is in the maximum illumination position, it is evident that the cell cannot be loaded to its maximum current rating. The second disadvantage is that the range of motion which can be transduced is limited by the size of the active face of the photocell. These disadvantages can be eliminated by using a special optical system, but this solution complicates the instrument and increases its cost, and thereby destroys two of its most desirable character= istics.

SUMMARY OF THE INVENTION The object of this invention is to provide a simple and relatively inexpensive photoelectric transducer which eliminates both of the disadvantages mentioned above. According to the invention, the transducer comprises a light source, a photocell, a movable illumination control element, and a block of transparent light-conducting material which is interposed between the control element and the photocell, and which is provided with a lightditfusing surface across which the control element moves light rays emitted by the source. The control element can be a vane which varies the area of the light-diffusing surface which is illuminated, or a movable light-transmitting slit which causes a bundle of light rays of constant cross section to move across the light-diffusing surface. In either case, the photocell is positioned along the path of movement of the light rays so that the amount of light energy it receives varies with movement of the control element. The light-conducting block insures uniform illumination of the entire active face of the photocell regardless of the intensity of illumination, and therefore the cells used in this transducer can always be loaded to their maximum current ratings. Furthermore, since the dimension of the light-conducting block in the direction of the path of movement of the light rays governs the range of travel of the control element, and it is much larger than the corresponding dimension of the active face of the photocell, it is evident that the invention increases greatly the range of motion which can be transduced.

DESCRIPTION OF THE DRAWINGS Several embodiments of the invention are' described herein with reference to the accompanying drawing in which:

FIG. 1 is a schematic diagram of the preferred embodiment of the invention.

FIG. 2 is a view taken on line 22 of FIG. 1.

FIG. 3 is a sectional view of an alternative sensing unit.

FIG. 4 is a schematic diagram showing an embodiment of a transducer employing a light vane.

FIG. 5 is a schematic diagram of an embodiment employing a dual photocell sensing unit.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The improved transducer shown in FIGS. 1 and 2 comprises an incandescent lamp 11, an illumination control element 12, which is moved in a vertical plane by the part (not shown) whose motion is to be transduced and which consists of an opaque plate containing an elon gated, rectangular aperture 13, and a sensing unit 14. Unit 14 includes a block 15 made of a transparent, lightconducting material, such as Lucite, and a photoconductive cell 16. Body 15 is a rectangular prism having a base 17 that defines a light-receiving or front surface which is normal to the light rays 18 passing through slot 13. Surface 17 is made translucent so that it diffuses incident light. This can be done easily by first polishing it to remove machining marks, and then rubbing it for a short time with emery cloth. The other five surfaces of body 14 are polished smooth, and then coated with black paint 19. Polishing increases internal reflection, and thereby minimizes light losses from the block, whereas the paint precludes entry into block 15 of stray light from the surrounding environment.

Photocell 16 is pressed into a bored and reamed hole 21 extending into block 15 from its back face 22. The hole terminates at a flat wall 23 which lies in a plane parallel with front surface 17 and is polished smooth. Hole 21 is located. adjacent the lower side face of block 15 on an axis which bisects block 15 and light slot 13, and which is parallel with the direction of movement of plate 12.

During operation, slot 13 in control plate 12 will transmit to the front surface 17 of block 15 an elongated bundle of light rays 18. Surface 17 diffuses this light over the entire cross section of block 15 so that some of the rays impinge directly on the wall 23 while others reach it after a series of internal reflections. Wall 23, and coning between the cell and the light bundle, the intensity of illumination of the photocell progressively increases. The photocell 16 used in the FIG. 1 embodiment is an A-35 photoconductive cell made by the General Electric Company, and its resistance is an inverse exponential function of illumination intensity. I have found that when block 15 is made relatively thick, and preferably has a thickness on the order of the range of. movement of plate 12, the relationship between plate movement and in tensity of illumination of the photocell is such that the cells resistance varies approximately linearly with plate movement.

Although the transducer of FIGS. 1 and 2 has proven satisfactory in actual use and is considered the preferred embodiment of the invention, it will be obvious that the inventive concept can take other forms. Three alternatives are shown in FIGS. 3-5. In the sensing unit 14a of FIG. 3, photocell 16a is mounted in a plate 24 which overlies the back face 22a of light-conducting block 15a in lieu of being mounted in the block itself. Plate 24 is opaque so it inherently prevents entry of stray light through back face 22a. In the FIG. 4 embodiment, the light control element takes the form of a vane 25 which is movable in a vertical plane by the part whose motion is to be transduced, and which serves to progressively vary the area of the front face 17 of block 15 which is illuminated by lamp 1]. This transducer operates in the same way as the one shown in FIG. 1, but, of course, here the cross section of light bundle 18 changes as the light rays are moved toward and away from photocell 16.

The transducer shown in FIG. 5 employs a sensing unit 14b containing two photocells 16b and 160, and is designed to sense direction as well as displacement. The slotted control plate 12 has a central position in which light bundle 18 is centered between the two photocells, and is movable up or down from that position as the controlling part is shifted in opposite directions from its reference position. This movement of plate 12 increases the light intensity at one of the walls 23b and 23c and decreases the intensity at the other wall, and thereby changes the resistances of the two photocells in opposite senses. The absolute change in the resistance of either cell is indicative of the amount of movement, and the relative values of the two resistances is indicative of the direction of movement. A transducer of this type is particularly useful in a null balance device.

While I have described several specific embodiments of the invention, it should be understood that the following claims provide the real measure of the scope of the invention.

I claim:

1. A photoelectric motion transducer comprising (a) a light source (11);

(b) a block (15, 15a or 15b) of light-conducting, transparent material having smooth surfaces except for an incident light-diffusing front surface (17 or 17a) which faces the source and is translucent by reason of being rough;

(c) an illumination control member (12 or 25) located between and movable relatively to the source and the block through a range of motion for causing light rays from the source to traverse the front surface of the block along a predetermined path, the transducer being free of opaque obstructions which would prohibit the passage of light from the control member into the block,

(d) the block having a rear surface (23, 23b, 230 or 2211) on which impinges light which passes through the block and at which the intensity of illumination varies progressively as light rays traverse said front surface; and

(e) at least one photocell (16) positioned along said predetermined path and arranged to sense light which. impinges on said rear surface, the dimension of the photocell measured in the direction of said path being substantially less than the corresponding dimension of the block; and

(f) means (19) associated with each surface of the block, except said front and rear surfaces, for re tarding the entry of stray light into the block.

2. The transducer defined in claim 1 in which the illumination control member is an opaque element (12) formed with a light-transmitting slit (13) through which light passes from the source (11) to the block (15), whereby the light rays (18 impinging on the front surface (17) of the block define a bundle of constant cross section.

3. The transducer defined in claim 1 in which the illumination control member is an opaque element (25) having an edge which is interposed in the light path between the source and the block and which moves in the direction of said predetermined path, whereby the light rays impinging on said front surface define a bundle having a variable cross section.

4. The transducer defined in claim 1 in which the means (19) for retarding entry of stray light is an adherent, opaque coating on the surfaces of the block.

5. The transducer defined in claim 1 in which (a) the block (15) is a rectangular prism having one base which constitutes said front surface (17);

(b) the photocell (16) is mounted in a bore (21) extending into the block from the second bace (22); and

(c) the bore (16) has a terminal wall (23) which con stitutes said rear surface.

6. The transducer defined in claim 1 in which (a) the block (15a) is a rectangular prism having one base which constitutes said front surface (17a);

(b) a portion of the second base (22a) constitutes said rear surface; and

(c) the photocell (16a) is mounted in a separate body (24) which overlies the second base.

7. The transducer defined in claim 1 in which (a) there are two photocells (16b and (b) the illumination control member (12) is an opaque element formed with a light-transmitting slit through which light passes from the source (11) to the block (15b), whereby the bundle of light rays which impinges on the front surface as a constant cross section; and

(c) the illumination control member causes the bundle of light rays (18) to move across said front surface (17b) in opposite directions from a position in which it is centered between the two photocells.

8. The transducer defined in claim 1 in which (a) the distance between said front and rear surfaces (17 or 17a and 23, 23b, 230 or 22a) is equal to the length of said range of motion; and

(b) the photocell (16, 16a, 16b or 160) has an output which varies approximately linearly with the relative movement between the control member 12 or 25) and the source (11) and block (1.5, 15a or References Cited UNITED STATES PATENTS 3,254,227 5/1966 Hock 250-232 X 1,680,756 8/1928 Winter 250233 X 2,883,649 4/1959 King 250-227 X 2,901,632 8/1959 Stava et al 250-227 X 3,062,964 11/1962 Lubin 250-227 3,121,795 2/1964 Marvin 250231 X 3,153,172 10/1964 Sun Ling 250227 X 3,360,657 12/1967 Shlesinger 250-227 ROBERT SEGAL, Primary Examiner US. Cl. X.R. 

